FIX wrong connection termination on start
NEW arbitrary per-pool start-up commands

Allow adding arbitrary post-connection start-up commands per pool. These
can be used to change state of all connections before issuing any
queries. For example, SQL_MODE, TIME_ZONE, etc.

Also add a bunch of environment tests.

Closes #43
Closes #78
Merge pull request #79 from spilgames/arbitrary_cmds

Arbitrary commands on pool startup